1. Field of the Invention
This invention relates to an instrument and method for administering retro-bulbar (or peri-bulbar) anesthetics. More specifically, a curved needle is disclosed which minimizes the attendant risk of such injection, commonly utilized in ocular surgery, such as cataract extraction, glaucoma filtering procedures, penetrating keratoplasty, repair of retinal detachment, and laser photocoagulation.
2. Description of the Prior Art
Needles used to date for retro-bulbar anesthetics have all been straight, of various lengths (the most popular currently approximately 38-50 mm), and calibers (most commonly 23 or 25 gauge). These needles have either been reusable or of the disposable type with pointed or rounded (Atkinson) tips.
The needle of the present invention differs from the needles which have been previously used to administer retro-bulbar anesthetics in that the needle of the present invention has a straight terminal section while the rest of the needle is curved.
While the prior art shows needles which are either angled with respect to the horizontal or are in some cases curved, none of these needles are suited for administering retro-bulbar or peri-bulbar anesthetics.
U.S. Pat. Nos. 4,013,080 and 4,511,356 to Froning et al disclose a needle having a curved terminal section for use in puncturing lumbar discs. Froning et al also discloses a vane for orienting the needle.
U.S. Pat. Nos. 762,603 to Witkowski and 4,518,383 to Evans disclose hypodermic needles which are angled from the central axis of the syringe.
U.S. Pat. Nos. 1,384,355 to Smith and 1,503,399 to Webb disclose hypodermic needles having some portion curved from the central axis of the hypodermic syringe.
While the prior art needles are similar in some respects to the hypodermic needle of the present invention, none of the patents cited disclose a needle suitable for use in administering retro-bulbar or peri-bulbar anesthetics, and none of these patents teach any method for such administration.
The present method of administering ophthalmic anesthesia is disclosed in the American Journal of Ophthalmology, Vol. 51, No. 1, January 1961, in an article by Walter S. Atkinson, M.D., entitled "The Development of Ophthalmic Anesthesia". The prior method, as described in the article, requires the insertion of the needle in the infero-temporal quadrant of the orbit with the needle being directed straight back well away from the eyeball until the point is beyond the globe. It is then pointed superiorly towards the apex of the orbit and inserted to a depth of 2.5-3.5 cm, and the injection is then made in the muscle cone.
The design of the present invention is advantageous in decreasing many of the risks of the common complications of the now utilized method of retro-bulbar injection.
One common complication is retro-bulbar hemorrhage which is reduced with the use of the needle of the present invention because less orbital space is violated. The straight needle of the prior art is passed posteriorly until the tip is posterior to the equator of the globe, and it is then angled superiorly as it is passed further posteriorly towards the apex of the orbit. Thus, a quasi-triangular planar space is violated by the needle. With the curved needle of the present invention, only a basically curvilinear space is violated with consequently less disruption of intra-orbital tissues and therefore vessels.
With the use of the needle of the present invention, there is less stress on the violated tissue. The tissue penetrated by the straight needle is stretched as the needle is lifted for passage in an increasingly superior direction. The shaft of the needle also may displace the globe superiorly as the tip is directed towards the apex, and this further adds to the tension placed on the intra-orbital vessels, thereby rendering them more susceptible to rupture. The curved needle does not "tent" or stretch the penetrated tissue, nor does it displace the globe in order to gain access to the muscle cone behind it. The curved needle passes around the globe.
Another advantage of the needle of the present invention is that there is increased distance from the central retinal artery and vein when the needle is inserted. The central retinal artery and vein approach the optic nerve infero-medially. The curved needle introduced infero-temporally passes more temporal than does the straight needle and, consequently, is further from the retinal artery and vein.
Furthermore, use of the needle and method of the present invention, reduces the possibility of injury to the optic nerve. The angulation of the straight terminal section of the needle of the present invention approximates the angle at which the optic nerve travels in the axial plane between the globe and the optic foramen. The approach of the needle tip is consequently more parallel to the optic nerve than is the straight needle used in the prior art which passes at a steeper angle superiorly than does the optic nerve.
In addition, the use of a needle with an arc of curvature greater than the arc of curvature of the eye renders penetration of the globe highly unlikely, given close attention to the technique of insertion.
The use of the needle of the present invention reduces the chance of the oculo-cardiac reflex. This "vaso-vagal reaction" is less likely to occur as a result of the decreased risks of retro-bulbar hemorrhage and the decreased tension upon the pre-paralyzed extra-ocular muscles by the displacement of the globe, as may occur to a small degree with conventional straight needles.